The present invention relates to a precious-metal material for articles of jewelry comprising precious metal powders and a non-metallic additive. The invention also relates to a method of manufacturing these materials and jewelry articles.
Throughout history, jewelry has been manufactured from precious metals such as gold, silver, platinum, palladium and particularly from alloys thereof. There are a number of known precious-metal alloys used for such purposes, the main component normally being the precious metal. Gold alloys in particular are classified as 8, 9, 14, 18 or 20-carat, i.e. depending on their gold content. An alloying of base metals is needed for improving the mechanical properties of the jewelry alloys, such as hardness and resistance to wear.
Some of these alloys contain heavy-metal constituents such as nickel or lead which can cause allergies. There is therefor a need for jewelry materials which are free from heavy metals.
Today the selling price of jewelry made from precious metals is closely dependent on the cost of the precious metals therein. The object of the jewelry industry, therefor, is to use materials with a low content of precious metals. These efforts, however, are limited by the fact that low-carat alloys (8 or 9 carats) have unsatisfactory physical and chemical properties, particularly a tendency to oxidation and corrosion.
DE-PS 31 35 034 (U.S. Pat. No. 4,476,090 which is incorporated by reference in its entirety) discloses a jewelry material containing a glass component in addition to precious metal. This material, however, has the disadvantage that only about 5 or 6 wt. % of glass can be added without drastically impairing the manufacturing properties of the material. In addition, due to the glass component, the material contains oxides of heavy metals such as lead, zinc or tin which can cause allergies.
Another object of the jewelry industry is to use lighter precious-metal materials and hollow articles of jewelry, such as earrings or pendants, so that they are lighter and more comfortable to wear. Electroplated hollow jewelry has become increasingly important in this sector in recent years. Methods of manufacturing electroformed hollow gold jewelry are described e.g. in DE-PS 33 09 397 (U.S. Pat. No. 4,487,664 which is incorporated by reference in its entirety). The general disadvantage of hollow jewelry, however, is that it has low strength and is easily deformed under impact and pressure. It also sounds hollow and tinny when struck.